Wind turbine foundation and method of constructing a wind turbine foundation

ABSTRACT

A wind turbine foundation and method for making a wind turbine foundation. The wind turbine foundation preferably includes a core member including a substantially cylindrically-shaped main body, a first outer flange extending out from the main body along an upper section of the core member, and a second outer flange extending out from the main body along a lower section of the core member, and a plurality of radial girders connected to the first outer flange and the second outer flange and radiating out from the core member.

CROSS-REFERENCE(S) TO RELATED APPLICATION(S)

This application is a nonprovisional of and claims priority to pendingU.S. Provisional Patent Application No. 62/741,184 entitled “WindTurbine Foundation” filed on Oct. 4, 2018 and pending U.S. ProvisionalPatent Application No. 62/874,029 entitled “WK Wind Turbine Foundation”filed on Jul. 15, 2019, both of which are incorporated herein byreference in their respective entireties.

FIELD

This disclosure relates to the field of construction related to windturbines or other tower-like structures. More particularly, thisdisclosure relates to a foundation for a wind turbine.

BACKGROUND

The wind energy generation market has experienced tremendous growth overthe past decade with wind energy currently recognized as the lowest costsource of renewable energy generation. The key driver of this growth hasbeen the advancements made in wind turbine technologies, with windturbines growing in capacity, size and height every year. Theadvancements in wind turbine technologies has placed increasing strainson the other classical approaches to wind project design andconstruction, and as a result several of the classical, brute forceapproaches to wind project design and construction are reaching theirlimits of effectiveness and cost efficiency. Change in wind projectdesign and construction is required to complement the turbine technologychanges being experienced in the industry.

In 2018 US wind energy generation capacity grew by over 8%, and theinstalled capacity of wind generation is anticipated to exceed that ofhydro by the end of 2020. This growth has been driven by the reductionsin cost of the wind generation technologies. The key driver of thesereductions in cost have been the advancements in wind turbinetechnologies. Wind turbines have grown consistently in the past fewyears with turbine size, weight and tower heights increasingsignificantly every year. In 2018 the largest turbines installed inNorth America had capacities on the order of 3.6 MW, with tower heightsof 110 m. In 2020 wind turbine installations will include 4.8 MWturbines with tower heights exceeding 140 m.

While turbine sizes are growing every year, turbine logistics remainconstrained with road, rail and truck transport limiting tower basedimensions. These increases in turbine size combined with limit ongrowth of the tower base dimensions has resulted in significant growthin the load demands being placed on the wind turbine foundations. Incontrast to the technology improvements seen on the turbines, windturbine foundation technologies have not advanced significantly over thepast 20 years. Today's predominant wind turbine foundations are thetraditional concrete raft foundation, with minor variations beingapplicable for unique ground conditions (shallow bedrock situations,etc.). While the concrete raft foundation was a good solution for theturbines installed in 2016, with capacities of 2.6 MW and tower heightsof 70 m, they are now approaching their limits of applicability.Increasing the size and strength of the concrete raft foundation is nota simple matter, with rebar and anchor bolt cage densities reaching thelimits of constructability, the complexities of very large concretepours creating significant logistics issues and quality risks. What isneeded therefore are new approaches to wind turbine foundations to meetthe needs of the continuing advancements in wind turbine technologies.

SUMMARY

The above and other needs are met by a wind turbine foundationcomprising a core member which may include, for example, a metal basecan or a metal spool. In some embodiments wherein the core membercomprises a metal base can, the metal base can further comprises asubstantially cylindrically-shaped main body, a first outer flangeextending out from the main body along an upper section of the base can,a second outer flange extending out from the main body along a lowersection of the base can, and a tower flange including a plurality ofapertures for attaching a wind turbine tower to the base can; and aplurality of metal radial girders connected to and radiating out fromthe base can wherein each of the plurality of radial girders areconnected to the first outer flange and the second outer flange.Preferably, the wind turbine foundation of claim 1 wherein the windturbine foundation is located in an excavated hole in the ground,wherein the hole in the ground is created by removing soil, and whereinat least some of the removed soil is laid over at least a portion of theplurality of metal girders. The wind turbine foundation preferablyfurther includes an underlying slab and a layer of rebar located abovethe underlying slab. The wind turbine foundation preferably furtherincludes a base layer of concrete poured along the underlying slab andthe layer of rebar.

In some embodiments, the plurality of radial girders includes an uppergirder flange and a lower girder flange wherein each upper girder flangeis connected to the first outer flange and each lower girder flange isconnected to the second outer flange.

In some embodiments, the wind turbine foundation includes an inner shellof concrete lining an inside surface of the base can. In similarembodiments, the wind turbine foundation may further include concretesubstantially filling the base can.

In some embodiments, the wind turbine foundation includes a reinforcedconcrete base slab supporting the metal base can and the plurality ofradial girders, wherein the excavation under the slab is tapered so thata bottom side of the slab filling the excavation is tapered and bulgesalong a middle portion of the base slab.

In some embodiments, the wind turbine foundation includes a reinforcedconcrete base slab wherein the excavation under the slab is in a steppedconfiguration so that a bottom side of the slab filling the excavationis in a stepped configuration.

In some embodiments, the wind turbine foundation includes a plurality offirst transverse girders wherein individual members of the plurality offirst transverse girders are located between and connected to pairs ofthe plurality of radial girders. The wind turbine foundation may furtherinclude a plurality of second transverse girders wherein individualmembers of the plurality of second transverse girders are locatedbetween and connected to pairs of the plurality of girders at distalends of the radial girders.

In some embodiments, the wind turbine foundation includes a perimetergrade beam of concrete and a mid-grade beam of concrete beneath areinforced concrete base slab.

In some embodiments, at least a first portion of the upper girderflanges are substantially parallel with a portion of the lower girderflanges. In some embodiments, the first portion of the upper girderflanges comprises most of the upper girder flanges.

In some embodiments the plurality of radial girders comprises aplurality of truss girders.

In some embodiments the wind turbine foundation includes a plurality ofpiles supporting the plurality of radial girders at distal ends of theplurality of radial girders.

In some embodiments the wind turbine foundation further includes a corecolumn inside the base can and a plurality of stiffener plates connectedto and radiating out from the core column wherein distal edges of thestiffener plates are connected to an interior surface of the base can.The wind turbine foundation may further include a first plurality ofrock anchors connected to the plurality of radial girders wherein thereis at least one rock anchor per radial girder extending into bedrock.The wind turbine foundation may further include a plurality oftransverse girders wherein individual members of the plurality oftransverse girders are located between and connected to pairs of theplurality of radial girders. The wind turbine foundation may furtherinclude a second plurality of rock anchors connected to the plurality oftransverse girders wherein there is at least one rock anchor pertransverse girder extending into bedrock. In some embodiments the basecan further comprises a plurality of vertical flanges wherein individualvertical flanges of the plurality of vertical flanges are connected toindividual radial girders of the plurality of radial girders.

In some embodiments the wind turbine foundation includes a plurality ofvertically oriented beams connected to an interior surface of the basecan to stiffen the base can.

In another aspect, a wind turbine foundation is disclosed comprising ametal spool; a plurality of metal radial girders connected to andradiating out from the metal spool; and a ring girder connected abovethe plurality of radial girders wherein the ring girder furthercomprises a tower flange including a plurality of apertures forattaching a wind turbine tower to the ring beam. The ring girder mayfurther include a composite ring girder comprising a plurality of ringgirder sections forming the composite ring girder wherein ring girdersections are individually connected to the plurality of radial girderswith one ring girder section per radial girder. The spool may furtherinclude a substantially cylindrically-shaped main body, a first outerflange extending out from the main body along an upper section of thespool, and a second outer flange extending out from the main body alonga lower section of the spool wherein each of the plurality of radialgirders are connected to the first outer flange and the second outerflange. The spool may further include a plurality of vertical flangeswherein individual vertical flanges of the plurality of vertical flangesare connected to individual radial girders of the plurality of radialgirders. The spool may further include a plurality of pairs of verticalflanges located in an area between the first outer flange and the secondouter flange wherein individual pairs of vertical flanges of theplurality of pairs of vertical flanges are connected to individualradial girders of the plurality of radial girders.

In another aspect, a method of making a wind turbine foundation isdisclosed, the method comprising the steps of excavating a foundationarea in the ground by removing excavated soil from the ground; pouring amud slab in the excavated foundation area to create a level worksurface; placing a metal core member in the excavated foundation area;and attaching a plurality of metal radial girders to the core member.The core member may include, for example, a metal base can or a metalspool. The core member preferably includes a substantiallycylindrically-shaped main body, a first outer flange extending out fromthe main body along an upper section of the core member, and a secondouter flange extending out from the main body along a lower section ofthe core member wherein each of the plurality of radial girders areconnected to the first outer flange and the second outer flange.

The summary provided herein is intended to provide examples ofparticular disclosed embodiments and is not intended to cover allpotential embodiments or combinations of embodiments. Therefore, thissummary is not intended to limit the scope of the invention disclosurein any way, a function which is reserved for the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, aspects, and advantages of the present disclosure willbecome better understood by reference to the following detaileddescription, appended claims, and accompanying figures, wherein elementsare not to scale so as to more clearly show the details, wherein likereference numbers indicate like elements throughout the several views,and wherein:

FIG. 1 shows a perspective view of an embodiment of a base can used inthe construction of wind turbine foundations described herein;

FIG. 2 shows a cutaway partial side view of a portion of a wind turbinefoundation showing a girder attached to the right side of the base canshown in FIG. 1 and, for illustrative purposes to better show featuresof the base can, with no girder shown attached to the left side of thebase can;

FIG. 2A shows a close-up view of a first highlighted section of the windturbine foundation shown in FIG. 2;

FIG. 2B shows a close-up view of a second highlighted section the windturbine foundation shown in FIG. 2

FIG. 2C shows a partial plan view of the wind turbine foundation shownin FIG. 2.

FIG. 3A shows a plan view of the wind turbine foundation shown in FIG. 2including a plurality of girders attached to a base can like the oneshown in FIG. 1;

FIG. 3B shows a full side view of the wind turbine foundation shown inFIG. 3A;

FIG. 4A shows a plan view of a wind turbine foundation including a solidconcrete center inside of a base can like the one shown in FIG. 1;

FIG. 4B shows a side view of the wind turbine foundation shown in FIG.4A;

FIG. 5A shows a plan view of a wind turbine foundation including noconcrete in the center of a base can like the one shown in FIG. 1;

FIG. 5B shows a side view of the wind turbine foundation shown in FIG.5A;

FIG. 6 shows a side view of a wind turbine foundation including atapered mud slab and base layer;

FIG. 7 shows a side view of a wind turbine foundation including atapered stepped mud slab and base layer;

FIG. 8A shows a plan view of a wind turbine foundation including aplurality of transverse girders between a plurality of girders;

FIG. 8B shows a side view of the wind turbine foundation shown in FIG.8A;

FIG. 9A shows a plan view of a wind turbine foundation including a baseslab (or base layer) including an inner beam and an outer beam;

FIG. 9B shows a side view of the wind turbine foundation shown in FIG.9A;

FIG. 10A shows a plan view of a wind turbine foundation includinggirders with a first tapered profile;

FIG. 10B shows a side view of the wind turbine foundation shown in FIG.10A;

FIG. 11A shows a plan view of a wind turbine foundation includinggirders with a second tapered profile;

FIG. 11B shows a side view of the wind turbine foundation shown in FIG.11A;

FIG. 12 shows a side view of a wind turbine foundation including aplurality of girder trusses;

FIG. 13A shows a plan view of a wind turbine foundation comprising abase can, a plurality of girders connected to the base can, and aplurality of piles supporting the plurality of girders with one pile pergirder;

FIG. 13B shows a side view of the wind turbine foundation shown in FIG.13A wherein the plurality of piles includes a plurality of screw piles;

FIG. 13C shows a side view of the wind turbine foundation shown in FIG.13A wherein the plurality of piles includes a plurality of concrete bellpiles;

FIG. 14A shows a plan view of a wind turbine foundation including a basecan including radial stiffeners inside the base can connected to acentral core member and the inside of the base can;

FIG. 14B shows a side view of the wind turbine foundation shown in FIG.14A;

FIG. 14C shows a partial plan view of the wind turbine foundation shownin FIG. 14A and FIG. 14B;

FIG. 14D shows a partial side view of the wind turbine foundation shownin FIGS. 14A-14C including a girder attached to the right side of thebase can and, for illustrative purposes to better show features of thebase can, with no girder shown attached to the left side of the basecan;

FIG. 14E shows a plan view of the base can used in the wind turbinefoundation shown in FIGS. 14A-14D;

FIG. 14F shows a segmented partial side view of the wind turbinefoundation shown in FIGS. 14A-14D wherein the image is cut and truncatedboth horizontally and vertically to show the top and bottom corners ofone side of the wind turbine foundation;

FIG. 14G shows a partial view looking down cut from a line shown in FIG.14F;

FIG. 15A shows a plan view of a wind turbine foundation including a basecan including vertical beams connected to the inside of the base can atlocations adjacent to where girders are connected to the base can;

FIG. 15B shows a side view of the wind turbine foundation shown in FIG.15A;

FIG. 16A shows a wind turbine foundation including a plurality ofgirders connected to a base can, transverse girders between andconnected to pairs of girders, and rock anchors connected to distal endsof the plurality of girders and along the transverse girders;

FIG. 16B shows a side view of the wind turbine foundation shown in FIG.16A;

FIG. 17A shows a plan view of a wind turbine foundation including aspool and a plurality of girders connected to the spool;

FIG. 17B shows a side view the wind turbine foundation shown in FIG. 17Awith a first tower piece added;

FIG. 17C shows a close-up partial plan view of the spool and theplurality of girders attached thereto from the wind turbine foundationshown in FIG. 17A;

FIG. 17D shows a cut-away side partial view of the spool and girdersfrom the wind turbine foundation shown in FIG. 17A;

FIG. 17E shows a cut-away partial view looking down from the center ofthe spool as viewed from line “FIG. 17E” shown in FIG. 17D;

FIG. 17F shows a cut-away partial view looking down a girder toward thespool as shown from the view of line “17F” in FIG. 17C wherein a ringbeam has been added to the apparatus from 17C and is bolted to theplurality of girders;

FIG. 17G shows a partial side view of a girder connected to a ringgirder which is connected to a first tower piece of the wind turbinefoundation shown in FIG. 17B;

FIG. 17H shows a cut-away partial view looking down a girder toward thespool wherein a curved ring girder section has been added by welding tothe girder shown in FIG. 17H;

FIG. 17I shows a partial side view of a girder welded to a ring beamwhich is attached to a first tower piece of the wind turbine foundation;and

FIG. 17J shows a close-up partial plan view of the spool, the pluralityof girders attached thereto from the wind turbine foundation shown inFIG. 17A and further shows a plurality of curved ring girder subsectionsconnected to the girders and forming a composite ring girder.

The figures are provided to illustrate concepts of the inventiondisclosure and are not intended to embody all potential embodiments ofthe invention. Therefore, the figures are not intended to limit thescope of the invention disclosure in any way, a function which isreserved for the appended claims.

DETAILED DESCRIPTION

An example of a wind turbine foundation 100 and its components is shownin FIGS. 1, 2, 2A, 2B, 2C, 2D, 3A and 3B. FIG. 1 shows a base can 102—acentral component of the wind turbine foundation 100 shown morecompletely in the plan view of FIG. 3A and a side view of FIG. 3B. Thebase can 102, which comprises a metal shell, is referred to as a “can”because of its preferred cylindrical shape which looks like atraditional can as well as its preferred composition (i.e., includingmostly or completely metal or metal alloy, hereinafter collectivelyreferred to as “metal”). A rounded cylindrically-shaped base can ispreferred but other shapes would work including a polygonal base canwith multiple faces. A plurality of radial girders 104 are connected tothe base can 102. The base can 102 preferably includes a first outerflange 106A and a second outer flange 106B. The plurality of girders 104are preferably connected to the base can 102 by bolting the girders 104to the first outer flange 106A and the second outer flange 106B.Although bolting is specifically described in this example, otherdevices and/or methods of attachment may be used such as, for example,welding.

The plurality of girders 104 preferably includes twelve substantiallysimilar girders of the same size and shape. In other examples, theplurality of girders 104 can include more than twelve or fewer thantwelve girders. The girders 104 and other similar objects describedherein are preferably made of steel but other metals or metal alloyscould be used instead of or in addition to steel. The girders 104 arepreferably made using traditional steel plate girder design used inbridge girders and existing steel bridge design codes and associatedmanufacturing methods. Each of the girders 104 is preferably tapered asshown and preferably has a length ranging from about 8 meters (m) toabout 14 m and a height at the highest point ranging from about 2.5 m toabout 5 m.

FIG. 2 shows a closer view of the base can 102 connected to a firstgirder 104A. A first close-up view of the connection between the firstouter flange 106A and the first girder 104A is highlighted and shown inFIG. 2A. A second close-up view of the connection between the secondouter flange 106B and the first girder 104A is also highlighted andshown in FIG. 2B. A plan view of the connections between the base can102 and the plurality of girders 104 is shown in FIG. 2C. The base can102 also preferably includes a tower flange 108 for attaching a firsttower piece 110 to the base can 102. A close-up view of a preferredconnection between the tower flange 108 and the first tower piece 110 ishighlighted and shown in FIG. 2A showing a preferred embodiment usingbolts on the inside of the base can 102 and the first tower piece 110but not on the outside. Other embodiments may include a two-sided towerflange for using both internal and external bolting to hold the base can102 to the first tower piece 110. Use of only internal bolts and only aninward facing tower flange is preferred because the mechanicalconnection is protected from the elements, thereby reducing corrosion orother deterioration of the connection between the base can 102 and thefirst tower piece 110. The base can 102 preferably has a diameter thatsubstantially matches the diameter of the first tower piece 110. Thewall thickness of the base can is preferably at least as thick as thewall thickness of the first tower piece 110.

The wind turbine foundation 100 preferably includes a mud slab 112 onwhich the base can 102 rests. The mud slab preferably comprises concretewith a level top surface and is preferably about 100 millimeters (mm) to150 mm thick in some embodiments. Rebar 114 and a base slab layer 116(preferably made of concrete) is preferably located above the mud slab112 inside and outside of the base can 102. The base slab layer 116 (or“base slab” or “base layer”) is designed at a nominal thickness that ismuch less than the mass concrete of a traditional raft foundation, thusavoiding prevalent heat-of-hydration and associated cracking andperformance concerns. The thickness of the base slab layer 116 isselected such that the required strength is achieved with a nominal,lower reinforcement ratio suitable to handle punching shear at the edgesof the girders 104. In some embodiments, the thickness of the base layer116 preferably ranges from about 300 mm to about 600 mm.

The girders 104 preferably include downward facing studs 118 (e.g.,Nelson™ studs) that are enmeshed with the rebar 114 and the base slablayer 116 and that are sized and spaced to provide sufficient steel tolimit the stress range to meet fatigue design requirements. Each of theplurality of girders 104 preferably includes upper girder flanges 120Aand lower girder flanges 120B as shown, for example, in FIG. 2.Preferably, the upper girder flanges 120A are bolted to the first outerflange 106A of the base can 102 and the lower girder flanges 120B arebolted to the second outer flange 106B of the base can 102. Each of theplurality of girders 104 also preferably includes a solid girder web 122and a plurality of stiffener plates 124. Crushed gravel 126 ispreferably placed directly adjacent to an upper section 128A of the basecan 102 at surface level, covering backfill 130 which is preferablyplaced along and/or above the girders 104 and base slab layer 116. Thebackfill 130 will principally be the excavated in situ materialsexcluding topsoil. Only in instances of saturated soils or unusual soilcomposition would imported material be required. Backfill will be placedin standard 200 mm to 300 mm lifts compacted to about 95% standardproctor maximum dry density or better to achieve a dense soil ballastover the entire foundation. The top of the base slab layer 116 isscreeded to the second outer flange 106B for convenience and to provideassurance of complete contact between the concrete and the underside ofthe second outer flange 106B. The lower girder flanges 120B preferablyinclude a plurality of “bleed holes” used to observe concrete flow underthe girders 104 for this purpose. Corrosion protection will vary basedon soil types but typically includes full epoxy coating of all steelcomponents and galvanized bolts, as well as a site-specific designedimpressed current grounding and monitoring system.

The radial girders 104 are proportioned at the base can 102 connectionbased on strength or stiffness. The girder 104 geometry is taperedtowards the outside perimeter to maintain a relatively constant sectioncapacity to resistance demand ratio. The can-ends of the girders 104(the ends of the girders 104 closest to the base can 102) have a shortand preferably substantially horizontal sections of the top flange tofacilitate the bolted connection to the can. This type of connection isselected because the first outer flange 106A (or “bolting ring”) on thebase can 102 also facilitates circumferential load distribution and ringstiffness acting as Tee Ring Beams. The connection is preferablydesigned as a “slip-critical” connection because shifting of the jointcould lead to incremental tower misalignment. The structural design ofthe girders 104 preferably follows typical practice for traditionalplate girders for bridges. In fact, in preferred embodiments, thegirders 104 and base slab layer of concrete 116 act as a CompositeRadial Inverted Bridge Section (CRIBS). The ends of the radial girders104 are preferably fitted with a support leg 111 including levellingbolt positioned over a steel plate on the mud slab 112 to facilitatelevel installation prior to concreting.

The embodiment of the wind turbine foundation 100 shown in FIG. 2through FIG. 3B includes an inner layer ring of concrete 132 locatedinside the base can 102. The ring of concrete 132 may further includerebar 134 included therein. Granular fill 136 (preferably compacted toat least or about 98% standard proctor maximum dry density) may be addedinside the ring of concrete 132. An example of the average size ofgranular fill that can be used in some embodiments is 40 mm.Additionally or alternatively, gravel could be added inside the ring ofconcrete 132 for added weight and to discourage water retention. Anotherlayer of rebar 138 and concrete 140 may be added above the ring ofconcrete 132 and the granular fill 136. In a different embodiment shownin FIGS. 4A and 4B, a wind turbine foundation 141 includes a fullconcrete core 142 located inside the base can 102. In the embodimentsshown in FIG. 2 through FIG. 4B, inward facing studs 144 (e.g., Nelson™studs) along the base can 102 are preferably included extending insidethe base can 102 enmeshed with concrete. Corrugated Steel Pipe (csp) 146is used to act as sacrificial steel form for the concrete.

FIGS. 5A and 5B show an embodiment of a wind turbine foundation 150including the base can 102 and the plurality of girders 104 but notincluding a concrete ring or concrete core inside the base can 102. Incertain embodiments, it may be preferably to minimize the use ofconcrete inside the base can 102.

FIG. 6 shows an embodiment of a wind turbine foundation 152 whereinground excavation 154 for the overall apparatus 152 is tapered. The windturbine foundation 152 preferably includes a tapered mud slab 156 havinga thickness preferably ranging from about 150 mm to about 300 mm. Abovethe mud slab 156 is a tapered base slab 158 which is preferably made ofconcrete and preferably reinforced with rebar. The base slab 158 isthickest beneath a base can 102 which is attached to a plurality ofgirders 104 in similar fashion to the wind turbine foundation 100described above with reference to FIG. 2 through FIG. 3B. The thicknessof the base slab 158 beneath the base can 102 preferably ranges fromabout 500 mm to about 1500 mm. The girders 104 include downward facingstuds 118 which are enmeshed with the base slab 158. Although taperedalong a peripheral section 160, a first portion of the base slab 162 ispreferably substantially flat beneath the base can 102.

FIG. 7 shows an embodiment of a wind turbine foundation 164 whereinground excavation 166 for the overall apparatus 164 is in a taperedstepped pattern. The wind turbine foundation 164 preferably includes atapered stepped mud slab 168 having a thickness preferably ranging fromabout 150 mm to about 300 mm. Above the mud slab 168 is a taperedstepped base slab 170 which is preferably made of concrete andpreferably reinforced with rebar. The base slab 170 is thickest beneatha base can 102 which is attached to a plurality of girders 104 insimilar fashion to the wind turbine foundation 100 described above withreference to FIG. 2 through FIG. 3B. The thickness of the base slab 170beneath the base can 102 preferably ranges from about 500 mm to about1500 mm. The girders 104 include downward facing studs 118 which areenmeshed with the base slab 170. In a preferred embodiment, the taperedstep pattern includes three steps from the periphery of the taperedstepped base slab to its center as shown in FIG. 7.

FIG. 8A and FIG. 8B show views of a wind turbine foundation 200including a mud slab 202, a base can 102 on or otherwise above the mudslab 202, a base slab 204 preferably made of concrete, and a pluralityof girders 104 connected to the base can 102. A peripheral section 206of the base slab 204 preferably extends deeper into the ground than acentral section 208 of the base slab 204. Additional features include aplurality of inner transverse girders 210 connecting midsections 212 ofadjacent radial girders 104 together and a plurality of outer transverse214 connecting outer sections 216 of adjacent radial girders 104together. The inner transverse girders 210 and outer transverse girders214 are preferably steel I-beams which are preferably bolted or weldedto adjacent girders 104 providing further structural support to the basecan 102 and girders 104. Use of the transverse girders in somecircumstances could allow for a thinner mud slab or an alternative typeof slab such as, for example, corrugated or ribbed steel panels orcomposite rigid panels. Granular backfill 218 preferably covers thegirders 104 and the base slab 204.

FIG. 9A and FIG. 9B show views of a wind turbine foundation 300including a mud slab 302, a base can 102 on or otherwise above the mudslab 302, a base slab 304 preferably made of concrete, and a pluralityof girders 104 connected to the base can 102. The base slab 304preferably includes an inner beam 306 and an outer beam 308 which bothextend deeper into the ground than the surrounding portions of the baseslab 304. The inner beam 306 is preferably beneath midsections 310 ofthe girders 104 and the outer beam is preferably beneath outer sections312 of the girders 104.

FIG. 10A and FIG. 10B show views of a wind turbine foundation 400 thatincludes a mud slab 202, a base can 102 on or otherwise above the mudslab 202, a base slab 204 preferably made of concrete reinforced withrebar, and a plurality of radial girders 406 connected to the base can102. The plurality of girders 406 are like the plurality of radialgirders 104 described above except for profile shape. The girders 406are preferably tapered as shown and the length of each of the girders406 preferably ranges from about 8 m to about 15 m and the height ofeach of the girders 406 at the highest point ranges from about 2.5 m toabout 5 m. In the example shown in FIG. 10A and FIG. 10B, rectangularsections 408 of the plurality of girders 406 extend out substantiallyhorizontally from about 20% to about 50% the length of each of thegirders 406 before angling downward along tapered sections 410. Inanother example, a wind turbine foundation 412 shown in FIG. 11A andFIG. 11B includes a plurality of radial girders 414 wherein rectangularsections 416 of the plurality of girders 414 extend out substantiallyhorizontally from about 50% to about 80% the length of each of thegirders 414 before angling downward along tapered sections 418 of thegirders 414. The girders 414 are preferably tapered as shown and thelength of each of the girders 414 preferably ranges from about 4 m toabout 12 m and the height of each of the girders 414 at the highestpoint ranges from about 2 m to about 5 m.

FIG. 12 shows a side view of a wind turbine foundation 500 that includesa mud slab 202, a base can 102 on or otherwise above the mud slab 202, abase slab 204 preferably made of concrete reinforced with rebar, and aplurality of radial girders 502 connected to the base can 102. Theplurality of girders 502 are like the plurality of girders 104 describedabove; however, the plurality of girders 502 shown in FIG. 12 includegirder trusses (open web girders) which allows for the plurality ofgirders 502 to be lighter than the formerly described plurality ofgirders 104 but maintain substantially the same level of strength. Eachof the girders 502 is preferably tapered and preferably has a lengthranging from about 8 m to about 15 m and a height at the highest pointranging from about 2.5 m to about 5 m.

FIG. 13A shows a plan view of a wind turbine foundation 600 including aleveling slab 602, a base can 102, and a plurality of radial girders 604connected to the base can 102. The plurality of girders 604 aresupported at distal ends 606 by a plurality of piles 608 extending intothe ground. Each of the girders 604 is preferably tapered and preferablyhas a length ranging from about 5 m to about 15 m and a height at thehighest point ranging from about 2 m to about 5 m. FIG. 13B shows anexample in which the plurality of piles 608 include helical piles 610.FIG. 13C shows an example in which the plurality of piles includeconcrete bell piles 612. In cases where there are soft soils near thesurface and stiffer soils or bedrock at depth using piles 608 to providesupport will sometimes be advantageous as opposed to making the overallfoundation much larger in diameter. Types of piles 608 that can be usedinclude, without limitation, pipe piles, H piles, helical screw pilesand concrete bell piles depending on the soil properties, groundwaterdepth and depth to the firm soils or bedrock. The piles 608 may be usedalone with just the radial girders (buried or not buried) such that noconcrete base slab is used. However, the piles may also be used incombination with a concrete base slab and buried as usual depending onthe soil characteristics, groundwater depth and load requirements. Inthe case of expanding clay soil in the upper soil strata, piles 608 maybe used in combination with a compressible foam panel or similar voidform placed under the mud slab, base slab or girders to prevent the soilexpansion from imposing uplift forces on the foundation.

The base can generally requires increased shear stiffness relative tothe towers above to provide overall rotational stiffness. In someembodiments, this is achieved by a combination of inner radialstiffeners 702 connected (preferably by welding) to the inside of a basecan 704 as required by site conditions and turbine manufacturerrequirements. For additional strength and support, concrete can be addedin the base can 704 between the radial stiffeners 702. An example of awind turbine foundation 700 including these features is shown in FIGS.14A-14G. FIG. 14A shows a plan view of the wind turbine foundation 700including the base can 704, inner radial stiffeners 702 connected to acentral core member 708 (e.g., a steel pipe) along proximal edges andconnected to the inside surface of the base can 704 along distal edges.The radial stiffeners 702 preferably include steel stiffener plateswhich can be connected to the base can 704 by, for example, welding orusing bolts.

FIG. 14B shows a side view, FIG. 14C shows a closer partial plan view,and FIG. 14D shows a closer partial side view of the wind turbinefoundation 700. FIG. 14E shows a plan view of the base can 704 byitself. FIG. 14F shows a close-up side view of the wind turbinefoundation 700 cut along a line revealing what is shown in FIG. 14G. Inthese various figures, different features are shown including a firstouter flange 710A near the top of the base can 704 and a second outerflange 710B near the bottom of the base can 704. A plurality of radialgirders 712 are connected to the base can 704. Each of the girders 712includes upper girder flanges 714A, lower girder flanges 714B, andgirder webs 716. Each of the girders 712 is preferably tapered as shownand preferably has a length ranging from about 8 m to about 15 m and aheight at the highest point ranging from about 2.5 m to about 5 m Thebase can 704 further includes a plurality of vertical flanges 718 whichextend between the first outer flange 710A and the second outer flange710B. The vertical flanges 718 are preferably situated directly adjacentto the girder webs 716 and first vertical plates 720A and secondvertical plates 720B are preferably situated on either side, overlappingthe vertical flanges 718 and the girder webs 716 such that, for example,bolts can be used to connect the vertical flanges 718, girder webs 716,first vertical plates 720A and second vertical plates 720B together. Aclose-up view of this is shown in FIG. 14G. In addition to thisconnection, the first outer flange 710A is preferably connected to theupper girder flanges 714A using, for example, bolts tightened throughfirst upper horizontal plates 722A and second upper horizontal plates722B as shown in FIG. 14F. Similarly, the second outer flange 710B ispreferably connected to the lower girder flanges 714B using, forexample, bolts tightened through first lower horizontal plates 724A andsecond lower horizontal plates 724B as shown in FIG. 14F.

The base can 704 further includes a tower flange 726 which preferablyextends inward and outward (like a “T”), preferably with at least tworows of apertures 728 through which bolts can be inserted to attach afirst tower piece 730 to the wind turbine foundation 700. The base can704 preferably includes upper stiffener plates 732 which preferablyextend from the first outer flange 710A to or near the tower flange 726and alternating partial stiffener plates 733 which alternate betweeninner radial stiffeners 702. The upper stiffener plates 732 arepreferably dispersed in line with girder webs 716 as well as spaces inbetween where girder webs 716 are angled toward the base can 704 asshown, for example, in FIG. 14E. The base can 704 and girders 712 arepreferably placed on support legs 734 including leveling bolts forleveling the base can 704 and girders 712 above rebar 736 on a mud slab738. After leveling is completed, a base layer 740 of concrete can bepoured. The girders preferably include downward facing studs 742 (e.g.,Nelson™ studs) that are enmeshed with the rebar 736 and the base layerbase layer 740 and that are sized and spaced to provide sufficient steelto limit the stress range to meet fatigue design requirements.

FIG. 15A and FIG. 15B show an embodiment of a wind turbine foundation800 including a base can 802 and a plurality of girders 712 connected tothe base can 802. Inside the base can 802, metal beams 804 (e.g., Hbeams) are connected (preferably by welding or field bolted) to aninside surface 806 of the base can 802 at locations adjacent to wheregirders 712 are connected to the base can 802. The base can 802 furtherincludes a first outer flange 808A near the top of the base can 802 anda second outer flange 808B near the bottom of the base can 802. Each ofthe girders 712 includes upper girder flanges 714A, lower girder flanges714B, and girder webs 716. The base can 802 further includes a pluralityof vertical flanges 810 which extend between the first outer flange 808Aand the second outer flange 808B. The vertical flanges 810 arepreferably situated directly adjacent to the girder webs 716 and firstvertical plates 720A and second vertical plates 720B are preferablysituated on either side, overlapping the vertical flanges 810 and thegirder webs 716 such that, for example, bolts can be used to connect thevertical flanges 810, girder webs 716, first vertical plates 720A andsecond vertical plates 720B together. A close-up view of this type ofconnection in a previous related embodiment is shown in FIG. 14G. Inaddition to this connection, the first outer flange 808A is preferablyconnected to the upper girder flanges 714A using, for example, boltstightened through first upper horizontal plates 722A and second upperhorizontal plates 722B. Similarly, the second outer flange 808B ispreferably connected to the lower girder flanges 714B using, forexample, bolts tightened through first lower horizontal plates 724A andsecond lower horizontal plates 724B. An example of these types ofconnections is shown in a previous embodiment shown in FIG. 14F.

The base can 802 further includes a tower flange 812 which, in thisembodiment, extends inward and outward (like a “T”), preferably with atleast two rows of apertures through which bolts can be inserted toattach a first tower piece 730 to the wind turbine foundation 800. Thebase can 802 and girders 712 are preferably placed on support legs 734including leveling bolts for leveling the base can 802 and girders 712above rebar 736 on a mud slab 738. After leveling is completed, a baselayer 740 of concrete can be poured. The girders preferably includedownward facing studs 742 (e.g., Nelson™ studs) that are enmeshed withthe rebar 736 and the base layer 740 and that are sized and spaced toprovide sufficient steel to limit the stress range to meet fatiguedesign requirements.

FIG. 16A and FIG. 16B show a different embodiment including a windturbine foundation 900 which would typically be used when suitablebedrock is close or at the surface at a location where a wind turbine isto be built. Depending on the rock characteristics and the degree ofrock weathering or quality, the foundation 900 may be either placed onthe surface without backfill or excavated and backfilled as perpreviously described foundation installations with a concrete base slabor not. Given the stronger rock qualities for bearing and support, thediameter of the overall foundation 900 would typically be smaller andthe forces would project out to the ends of a plurality of radialgirders 902. As such, in preferred embodiments, the girders 902 wouldnot be tapered like those of the pure gravity base versions describedabove. The foundation 900 preferably includes the base can 704 includingradial stiffeners 702, central core member 708, first outer flange 710A,second outer flange 710B, and vertical flanges 718. The girders 902 arepreferably connected to the base can in the same manner as theconnection between the girders 712 and the base can 704 shown in FIGS.14A-14G.

The girders 902 include rock anchors 904 at distal ends 906 of thegirders 904 wherein the anchors 904 penetrate into surrounding bedrock.The rock anchors 904 will be drilled in place to a depth suitable tomeet the uplift force requirements according to the rock mechanics andbonding design, and some consolidation grouting of the surrounding rockalso may be required. Typically, a double corrosion protected groutedbar anchor will be used in this application with post tensioning.However, a multi-strand cable anchor or multiple bar anchor with somecanting could also be deployed. Rock anchor heads 908 at the top of therock anchors 904 preferably would be designed to be accessible to checktheir post tensioning from time to time and the anchor heads 908preferably will be corrosion protected with removable caps and grease ora similar system. The wind turbine foundation 900 also preferablyincludes a plurality of transverse girders 910 preferably connectedbetween at the ends 906 of the girders 902. Preferably, one or more rockanchors 904 are also connected to the transverse girders between theradial girders 902.

In another aspect, an embodiment of a wind turbine foundation 1000 andassociated parts is shown in FIGS. 17A-17G. Instead of a wide base canwith a diameter substantially the same a bottom tower piece, the windturbine foundation 1000 has a narrower spool 1002 which preferablyincludes a metal cylindrical pipe including a top horizontal flange1004A, a bottom horizontal flange 1004B, and a plurality of verticalflanges 1006. The top horizontal flange 1004A and the bottom horizontalflange 1004B preferably extend out from the spool 1002 from about 2 m toabout 6 m. The spool height preferably ranges from about 2.5 m to about5 m. A plurality of girders 1008 are connected to the spool 1002preferably using bolts along the top horizontal flange 1004A, a bottomhorizontal flange 1004B, and a plurality of vertical flanges 1006. Thegirders 1008 preferably have a length ranging from about 9 m to about 18m and a maximum height ranging from about 2.5 m to about 5 m. The toweris mounted directly above the top of the girders themselves. The girdersinclude upper girder flanges 1010A, lower girder flanges 1010B, andgirder webs 1012. The upper girder flanges 1010A are connected to thetop horizontal flange 1004A, the lower girder flanges 1010B areconnected to the bottom horizontal flange 1004B, and the girder webs1012 are connected to the vertical flanges 1006. As one example, thevertical flanges 1006 are preferably situated in pairs defining aplurality of slits 1014 wherein each pair includes a slit between eachof the vertical flanges making up that particular pair of verticalflanges 1006. Portions of the girder webs 1012 along proximal ends 1016of the girders are slid into the slits 1014 and the girder webs 1012 areconnected to the pairs of vertical flanges 1006 preferably using bolts.The upper girder flanges 1010A along proximal ends 1016 of the girders1008 are preferably tapered so that the girders 1008 can be connected tothe spool 1002 in radial fashion as shown, for example, in FIG. 17C.

The girders 1008 preferably include curved flanges 1018 which arepreferably an extension of the upper girder flanges 1010A at a locationalong the girders 1008 above which a first tower piece 1019 would rest.The curved flanges 1018 together form a circle as shown, for example, inFIG. 17C. In one embodiment, a ring girder 1020 is placed above andconnected to the curved flanges 1018 as shown, for example, in FIGS. 17Band 17F-17I. In this embodiment, the ring girder 1020—preferably a shortcylinder of metal including an upper ring girder flange 1021 and a lowerring girder flange 1022—is bolted to the curved flanges 1018 along thelower ring girder flange 1022. The first tower piece 1019 is connectedto the ring girder 1019 along the upper ring girder flange 1021. In analternative embodiment shown in FIGS. 17H-17I, curved ring girdersubsections 1023 are welded directly to the upper girder flanges 1010Ainstead of using the curved flanges 1018. In this alternate embodiment,there is preferably one ring girder subsection welded to each girder(one ring girder subsection per girder). When all girders 1008 areassembled in place (i.e., connected to the spool 1002), the curved ringgirder subsections 1023 form a composite ring girder 1024 similar to thering girder 1020. The curved ring girder subsections 1023 include upperring girder subsection flanges 1025 for connection with the first towerpiece 1019. FIG. 17J shows a plan view of the plurality of girders 1008connected to the spool 1002 and including curved ring girder subsections1023 connected to the radial girders 1008 to form the composite ringgirder 1024 including the upper ring girder subsection flanges 1025 forconnecting a tower piece to the composite ring girder 1024.

In these examples, the girders 1008 include tapered stiffener plates1026. The stiffener plates 1026 are wide and are added to support thecurved flange 1018 (if present), the ring girder 1020, and/or thecomposite ring girder 1024 and distribute the tower forces to the fullgirder 1008 height.

During installation, the spool 1002 and girders 1008 are supported bysupport legs 1027 including leveling bolts. The support legs 1027 reston a mud slab 1028. A base layer 1030, preferably of reinforcedconcrete, is laid above the mud slab 1028, beneath the spool 1002 andgirders 1008. The girders 1008 preferably include downward facing studs1032 (e.g., Nelson™ studs) that are enmeshed with the base layer 1030and that are sized and spaced to provide sufficient steel to limit thestress range to meet fatigue design requirements. The wind turbinefoundation 1000 provides a stiffer direct connection between the towerpiece 1019 and the radial girders 1008 with the center girder connectiondone in a lower stress location reducing bolting and plate thicknessesas well as lessening fatigue issues. This configuration also provides amore direct load flow along each radial girder 1008 set from thecompression side to the tension side of the foundation 1000.

An example of a construction sequence for certain embodiments describedherein is as follows:

1. Excavate foundation area (e.g., ˜3 m×20 m diameter), verify in situground conditions and improve as per normal foundation preparation.2. Pour concrete mud slab to protect the exposed ground and create alevel work surface.3. Install base slab reinforcing over entire area noting the pattern forfoundation orientation.4. Install base can or spool on support legs which include levelingbolts.5. Install all radial girders by bolting to the base can or spool. Finallevelling of the tower flange is conducted by adjustment of thelevelling bolts on the girder ends and base can or spool perimeter. Theperimeter levelling bolts are used to perform final levellingadjustments to the tower flange. The levelling bolts on the base can orspool are raised during this process and re-lowered once the finallevelling is complete.6. Pour the base slab concrete and screed to the top of the second outerflange (girder base flange) ensuring full concrete contact to undersideof flange by watching the air bleed holes in the flanges.7. Install electrical conduits and grounding cables.8. Pour concrete fill in base can (if applicable) and trowel finish topsurface.9. Backfill foundation with excavated soil stockpiled adjacent to thearea.10. Grade area for drainage, install gravel surfacing and installprecast stairs foundation.

In one specific nonlimiting example, the wind turbine foundation 100 ispreferably housed in a hole dug in the ground with a preferred height offrom about 2 meters to about 4 meters and diameter of from about 15meters to about 25 meters for use with a 3.5 megawatt (MW) wind turbine.Although specific preferred dimensions are provided herein for anexample of a foundation for use with a 3.5 MW wind turbine, it should beunderstood that the technology described herein can be scaled withdifferent dimensions to accommodate different sized wind turbines.Digging the hole is a first step (A1) in building the wind turbinefoundation 100. An additional step (B1) includes pouring an underlyingmud slab 112 in the hole wherein, in this specific example, theunderlying mud slab 112 is preferably from about 50 mm to about 200 mmthick. The base can 102 and girders 104 are preferably situated on themud slab 112 that, in this specific example, is preferably round with adiameter of from about 15 meters to about 25 meters and most preferablyabout 20 meters. In this specific example, the girders 104 arepreferably about 2 meters tall along the tallest edge of the girders 104where the girders 104 attach to the base can 102, however other sizesare contemplated for different embodiments.

An additional step (C1) in making the wind turbine foundation 100includes placing the base can 102 in the hole on the underlying mud slab112. The base can 102 is preferably placed at the approximate center ofthe underlying mud slab 112. In this specific example, the base can 102is preferably from about 2 meters to about 6 meters high and mostpreferably about 3.5 meters high. In this specific example, the base can102 is preferably about 4 meters to about 6 meters in diameter and mostpreferably about 5 meters in diameter. The base can 102 preferablyincludes a collector port 172 through which electrical and potentiallyother connections can be made to a wind turbine resting on the windturbine foundation 100.

An additional step (D1) includes placing rebar 114 in the hole along theunderlying mud slab 112. The rebar 114 preferably has a diameter ofabout 20 mm, a linear mass density of about 2.4 Kg/m and across-sectional area of about 300 mm² but other rebar sizes may be used.In this specific example, the total weight of rebar used per windturbine foundation should be from approximately 10,000 Kg to about16,000 Kg and most preferably less than about 13,000 Kg.

Another step (E1) includes attaching the girders 104 to the base can 102preferably using bolts. In a following step (F1), a base layer ofconcrete 116 is poured beneath the girders 104 and beneath the base can102. In this specific example, preferably from about 100 m³ to about 120m³ of concrete is used to form the base layer 116.

A next step (G1) includes placing a mass of material (e.g., backfill 128from the excavation to dig the hole) above the base layer 116 andpreferably up to the collector port 172. Another step (H1) includesinstalling a collector conduit bundle 174 preferably through a culvert.

Another step (I1) includes adding additional backfill to the hole andinside the base can 102. Preferably, the backfill is added to aconsistent depth across the hole with a slight slope of from about 2% toabout 5% away from an upper section 128A of the base can 102 thatremains exposed. In another step (J1), additional rebar is added insidethe base can 102. A following step (K1) includes pouring concrete intothe base can 102 to form a base can slab 176 wherein, in this specificexample, from about 1 m³ to about 3 m³ of concrete is used. Another step(L1) includes attaching the first tower piece 110 to the tower flange108 along the upper section 128A of the base can 102. The first outerflange 106A extends out from a main body 178 of the base can 102 and isalso located along the upper section 128A of the base can 102. Thesecond outer flange extends out from the main body 178 of the base can102 and is located along a lower section 128B of the base can 102. As anexample, the first outer flange 106A and the second outer flange 106Bmay be welded to the main body 178 or may be formed as a part of thebase can 102.

In an embodiment where the base can is replaced by a spool, theplacement of the spool, the installation of rebar, the attachment of thegirders to the spool, the pouring of the concrete base layer, theplacing of the mass of material including installation of a collectorconduit and additional backfilling of the spool follow similar steps asoutlined above with the base can being replaced by the spool.

The previously described embodiments of the present disclosure have manyadvantages. As described in the Background section, current methods ofmaking foundations for wind turbines of the 3.5 MW size typically useabout 400 m³ of concrete, 83,000 Kg of steel, require a 5 week buildcycle, and, depending on the geographic location, can only be built forcertain months out of the year. For example, in many parts of Canada,construction can only be best carried out for about 8 months out of theyear. Some of the embodiments described herein relating to 3.5 MWturbines typically use about 140 m³ of concrete and 70,000 Kg of steel.Some of these embodiments described herein have a three week buildcycle, and can be built all twelve months of the year regardless ofgeography since many of the components including the girders can be madeoffsite during colder or otherwise inclement months. Current methods formaking foundations for 3.5 MW wind turbines require on average about 80truckloads of material. Some of the embodiments described hereinrelating to 3.5 MW turbines require approximately 20 truckloads ofmaterial since much of the ballast used is backfill from the initialexcavation (which, therefore, does not need to be hauled away).

The various embodiments preferably use pre-fabricated structural steelcomponents for efficient load transfer and distribution as part of thefoundation. Such embodiments maximize use of natural in-situ materials(e.g., excavated soil) to provide stability. The embodiments describedherein do not use a pre-tensioned anchor bolt cage embedded in concretefor transferring load from the tower to the foundation. Eliminating theanchor bolt cage eliminates a major construction step and makes rebarplacement easier. A bolted flange connection eliminates the entireanchor cage typically consisting of about 180 4 m long×40 mm bolts andassociated steel anchor rings. Embodiments described herein have adesign type that is a raft foundation, like a traditional concrete raftfoundation, however instead of concrete providing part of the bendingand shear resistance and most of the ballast, the embodiments describedherein use radial girders connected to a base can or spool for primaryload transfer and use mostly backfill as ballast over the thin concretebase slab. The loads transferred to the girders are distributed into theproximal parts of the concrete slab. The slab is held in place bybearing on the subgrade below and the weight of the backfill on top ofit. Similar to traditional concrete raft foundations, in medium to lowstrength soil conditions, the design is typically governed by rotationalstiffness, depending on the turbine manufacturer requirement forstiffness. In stronger soils and on bedrock, the foundation size tendsto be governed by overturning stability and sometimes bearing capacity.

New 4+ MW wind turbines forces and diameters are causing design limitsto be reached for traditional concrete raft foundations so analternative to such foundations is becoming more necessary. High shear,rebar spacing issues and high-strength concrete are now common. Siteconditions are dictating multiple traditional foundation solutions thatincrease cost and logistical challenges. For example, high groundwaterand shallow weak bedrock are often found. One foundation type—auniversal solution—is better than two or three different foundationtypes on one site from an economies-of-scale andsimplicity-of-construction perspective. Pre-fabricated foundations offeryear-round construction opportunity which decreases build time andreduces constraints. Shop manufactured components can be built andshipped any time of the year. In embodiments described herein, the towerto foundation joint is a bolted steel flange connection instead of agrouted base and anchor bolt connection. As turbine sizes increase,grouted connections are now reaching their maximum capacity. Boltedsteel flanges offer much higher capacity that are in concert with theother tower connections above and have much better fatigue performance.

The foregoing description of preferred embodiments of the presentdisclosure has been presented for purposes of illustration anddescription. The described preferred embodiments are not intended to beexhaustive or to limit the scope of the disclosure to the preciseform(s) disclosed. Different features of some embodiments can besubstituted for other features of other embodiments to arrive atdifferent embodiments of the concepts described herein. Obviousmodifications or variations are possible in light of the aboveteachings. The embodiments are chosen and described in an effort toprovide the best illustrations of the principles of the disclosure andits practical application, and to thereby enable one of ordinary skillin the art to utilize the concepts revealed in the disclosure in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such modifications and variations arewithin the scope of the disclosure as determined by the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally, and equitably entitled.

What is claimed is:
 1. A wind turbine foundation comprising: a. a metalbase can further comprising: i. a substantially cylindrically-shapedmain body, ii. a first outer flange extending out from the main bodyalong an upper section of the base can, iii. a second outer flangeextending out from the main body along a lower section of the base can,and iv. a tower flange including a plurality of apertures for attachinga wind turbine tower to the base can; and b. a plurality of metal radialgirders connected to and radiating out from the base can wherein each ofthe plurality of radial girders are connected to the first outer flangeand the second outer flange.
 2. The plurality of radial girders of claim1 wherein each of the plurality of radial girders comprises an uppergirder flange and a lower girder flange and wherein each upper girderflange is connected to the first outer flange and each lower girderflange is connected to the second outer flange.
 3. The wind turbinefoundation of claim 1 wherein the wind turbine foundation is located inan excavated hole in the ground, wherein the hole in the ground iscreated by removing soil, and wherein at least some of the removed soilis laid over at least a portion of the plurality of metal girders. 4.The wind turbine foundation of claim 3 further comprising an underlyingslab and a layer of rebar located above the underlying slab.
 5. The windturbine foundation of claim 4 further comprising a base layer ofconcrete poured along the underlying slab and the layer of rebar.
 6. Thewind turbine foundation of claim 1 further comprising an inner shell ofconcrete lining an inside surface of the base can.
 7. The wind turbinefoundation of claim 1 further comprising concrete substantially fillingthe base can.
 8. The wind turbine foundation of claim 1 furthercomprising a reinforced concrete base slab supporting the metal base canand the plurality of radial girders, wherein the excavation under theslab is tapered so that a bottom side of the slab filling the excavationis tapered and bulges along a middle portion of the base slab.
 9. Thewind turbine foundation of claim 1 further comprising a reinforcedconcrete base slab wherein the excavation under the slab is in a steppedconfiguration so that a bottom side of the slab filling the excavationis in a stepped configuration.
 10. The wind turbine foundation of claim1 further comprising a plurality of first transverse girders whereinindividual members of the plurality of first transverse girders arelocated between and connected to pairs of the plurality of radialgirders.
 11. The wind turbine foundation of claim 10 further comprisinga plurality of second transverse girders wherein individual members ofthe plurality of second transverse girders are located between andconnected to pairs of the plurality of girders at distal ends of theradial girders.
 12. The wind turbine foundation of claim 1 furthercomprising a perimeter grade beam of concrete and a mid-grade beam ofconcrete beneath a reinforced concrete base slab.
 13. The wind turbinefoundation of claim 1 wherein at least a first portion of the uppergirder flanges are substantially parallel with a portion of the lowergirder flanges.
 14. The wind turbine foundation of claim 1 wherein thefirst portion of the upper girder flanges comprises most of the uppergirder flanges.
 15. The wind turbine foundation of claim 1 wherein theplurality of radial girders comprises a plurality of truss girders. 16.The wind turbine foundation of claim 1 further comprising a plurality ofpiles supporting the plurality of radial girders at distal ends of theplurality of radial girders.
 17. The wind turbine foundation of claim 1further comprising a core column inside the base can and a plurality ofstiffener plates connected to and radiating out from the core columnwherein distal edges of the stiffener plates are connected to aninterior surface of the base can.
 18. The wind turbine foundation ofclaim 17 further comprising a first plurality of rock anchors connectedto the plurality of radial girders wherein there is at least one rockanchor per radial girder extending into bedrock.
 19. The wind turbinefoundation of claim 18 further comprising a plurality of transversegirders wherein individual members of the plurality of transversegirders are located between and connected to pairs of the plurality ofradial girders.
 20. The wind turbine foundation of claim 19 furthercomprising a second plurality of rock anchors connected to the pluralityof transverse girders wherein there is at least one rock anchor pertransverse girder extending into bedrock.
 21. The wind turbinefoundation of claim 17 wherein the base can further comprises aplurality of vertical flanges wherein individual vertical flanges of theplurality of vertical flanges are connected to individual radial girdersof the plurality of radial girders.
 22. The wind turbine foundation ofclaim 1 further comprising a plurality of vertically oriented beamsconnected to an interior surface of the base can to stiffen the basecan.
 23. A wind turbine foundation comprising: i. a metal spool; ii. aplurality of metal radial girders connected to and radiating out fromthe metal spool; and iii. a ring girder connected above the plurality ofradial girders wherein the ring girder further comprises a tower flangeincluding a plurality of apertures for attaching a wind turbine tower tothe ring beam.
 24. The wind turbine foundation of claim 23 wherein thering girder further comprises a composite ring girder comprising aplurality of ring girder subsections forming the composite ring girderwherein ring girder subsections are individually connected to theplurality of radial girders with one ring girder subsection per radialgirder.
 25. The wind turbine foundation of claim 23 wherein the spoolfurther comprises a substantially cylindrically-shaped main body, afirst outer flange extending out from the main body along an uppersection of the spool, and a second outer flange extending out from themain body along a lower section of the spool wherein each of theplurality of radial girders are connected to the first outer flange andthe second outer flange.
 26. The wind turbine foundation of claim 23wherein the spool further comprises a plurality of vertical flangeswherein individual vertical flanges of the plurality of vertical flangesare connected to individual radial girders of the plurality of radialgirders.
 27. The wind turbine foundation of claim 23 wherein the spoolfurther comprises a plurality of pairs of vertical flanges located in anarea between the first outer flange and the second outer flange whereinindividual pairs of vertical flanges of the plurality of pairs ofvertical flanges are connected to individual radial girders of theplurality of radial girders.
 28. A method of making a wind turbinefoundation, the method comprising the steps of: i. excavating afoundation area in the ground by removing excavated soil from theground; ii. pouring a mud slab in the excavated foundation area tocreate a level work surface; iii. placing a metal core member in theexcavated foundation area; and iv. attaching a plurality of metal radialgirders to the core member.
 29. The method of claim 28 wherein the coremember comprises a member selected from the group consisting of a metalbase can and a metal spool.
 30. The method of claim 28 wherein the coremember comprises a substantially cylindrically-shaped main body, a firstouter flange extending out from the main body along an upper section ofthe core member, and a second outer flange extending out from the mainbody along a lower section of the core member wherein each of theplurality of radial girders are connected to the first outer flange andthe second outer flange.